Analytical Physical Practica High performance liquid chromatography Version 1, Group M14 Jorge Ferreiro, Studiengang Chemieingenieur 4. Semester, fjorge@student.ethz.ch Natalja Früh, Studiengang Interdisziplinäre Naturwissenschaften 4. Semester, fruehn@student.ethz.ch Arman Nilforoushan, Studiengang Chemieingenieur 4. Semester, armanni@student.ethz.ch Assistent: Liang Zhu Zürich, 19. Mai 2009 Jorge Ferreiro Natalja Früh Arman Nilforoushan
1. Theory High performance liquid chromatography is a separation method, where the analytes in the mobile phase are pushed through a stationary phase at a high pressure (up to 300 bar). The affinity of the analytes to the stationary phase decides how fast the molecules run through the column. These various passing times are called times. The size-exclusion-chromatograph sizes the molecules according to their largeness: small molecules dip deeper into the matrix of the stationary phase therefore the time is bigger. The polarity-chromatograph separates the molecules due to their polarity. The stationary phase usually consists of polar silica gel, or in this case by silica gel modified by long alkane chains what makes it non-polar. The mobile phase is chosen based on the stationary phase, it has always opposite polarity. 1.1. Chromatographic parameters Parameter dead time t 0 time t R net time t R capacity ratio k relative a i,j number of separation steps Explanation time a component that does not interact with any phase of the column needs to pass through the column time a (interacting) component needs to pass through the column difference between a component s time and the column dead time (1), (2) indicator for the quality of a certain measurement 16 where ω is the width of the peak Tab. 1: explanation of several chromatographic parameters (3)
2. Experimental 2.1. Experimental setup Fig. 1: experimental setup The used system contains different components: System controller SCL-10A Diode array detector SPD-10A VP Liquid chromatograph LC-10A VP Degasser DGU-14A Vacuum pump VCV-10AL VP All these components are from the manufacturer Shimadzu. Mobile phase flow rate: 1 ml/min Column pressure: 94 bar 2.2. Chemicals Name Composition Structure R-Sentences S-Sentences Acetonitrile CH 3 CN 11-20/21/22-36 (1/2)-16-36/37 Water H 2 O - - Acetophenone C 8 H 8 O 22-36 (2)-26 Propiophenone C 9 H 10 O n-butyrophenone C 10 H 12 O
n-valerophenone C 11 H 14 O caffeine C 8 H 10 N 4 O 2 22 (2) poly(methacryl acid Sodium Salt) humic acid 36/37/38 26-36 Tab. 2: Chemicals 2.3. Influence of the composition of the eluent: qualitative interpretation of the chromatogram of a homolog phenone-series A dilution of acetophenone, propiophenone, n-butyrophenone and n-valerophenone was already prepared for the experiment. For each measurement 20 μl of the dilution were injected in the apparatus. Three different eluent mixtures were measured to find the perfect ratio between acetonitrile and water. The mixture was set up by a program: a) 50% acetonitrile, 50% water (program: PHE50.MET) b) 60% acetonitrile, 40% water (program: PHE60.MET) c) 70% acetonitrile, 30% water (program: PHE70.MET) For every mixture one chromatogram was measured, between the measurements the column was rinsed with the new eluent mixture for five minutes. 2.4. Determination of the concentration of an unknown solution of acetophenone with internal standard To determine the concentration of an unknown solution of acetophenone propiophenone was used as internal standard. To calibrate three different solutions of acetophenone in acetonitrile and water (1:1) were prepared: 20 mg/l, 40 mg/l, and 60 mg/l. To each of these solution 20 mg/l propiophenone was added as internal standard. The concentration of the unknown solution was 45 mg/l. For each solution three measurements were done, the detection took place at a wavelength λ=250 nm. For each measurement 20 μl of the solution were injected in the apparatus. The measurement was started by a program (ACINS.MET). 2.5. Quantitative analysis of caffeine in ice tea and espresso Three different calibration solutions were prepared: 0.095 g/l, 0.075 g/l, 0.045 g/l caffeine in acetonitrile (15%) and water (85%). Each of the solutions was measured three times. The coffee was filtered using a 0.2 μm cellulose filter and diluted with nanopure water (1:39). The ice tea was measured as it was.
2.6. Size exclusion chromatography 2.6.1. Calibration of the column with polymethacryl acid (PMA) Three different standards of PMA with molecular weight 1270 Da, 4030 Da, and 7750 Da were prepared. A spatula of the polymer was put in an eppendorf and filled up with nanopure water. Before the analysis the solutions were filtered using a 0.2 μm cellulose filter. The same set up as described in 2.1. was used, but instead of the standard column a size exclusion Waters Ultrahydrogel 120 column was used. 2.6.2. Measurement of a humic acid standard Humic acid of two different manufacturers (Aldrich, Fluka) were analysed, as humic acid is a very complex acid. Two solutions were prepared: A spatula of the humic acid was put in an eppendorf and filled up with nanopure water. This solution was filtered using a 0.2 μm cellulose filter and diluted with nanopure water until the colour was light yellow. Each solution was measured once with the same set up as described in 2.6.1.. 3. Results 3.1. Influence of the composition of the eluent: qualitative interpretation of the chromatogram of a homolog phenon-series net capacity ratio peak width [min] number of separation steps Acetophenone 3.816 2.816 2.816 0.326 2192.3 28625177 Propiophenone 5.207 4.207 4.207 0.538 1498.8 28642237 n-butyrophenone 7.368 7.368 7.368 0.475 3849.7 25810022 n-valerophenone 10.984 9.984 9.984 1.0215 1850.0 17155821 Tab. 3: Results for 50% acetonitrile, 50% water relative resolution a 12 1.494 R 12 3.220 a 23 1.751 R 23 4.267 a 43 1.355 R 34 4.833 Tab. 4: Results for 50% acetonitrile, 50% water net capacity ratio peak width [min] number of separation steps Acetophenone 3.101 2.101 2.101 0.238 2716.2 23343536 Propiophenone 3.827 2.827 2.827 0.282 2946.7 23193449 n-butyrophenone 4.776 3.776 3.776 0.305 3923.28 20938711 n-valerophenone 6.296 5.296 5.296 0.362 4839.9 15339444 Tab. 5: Results for 60% acetonitrile, 40% water relative resolution a 12 1.346 R 12 2.792 a 23 1.336 R 23 3.233 a 43 1.403 R 34 4.558 area area
Tab. 6: Results for 60% acetonitrile, 40% water net capacity ratio peak width [min] number of separation steps Acetophenone 2.717 1.717 1.717 0.256 1802.3 21674502 Propiophenone 3.112 2.112 2.112 0.266 2190.0 20957056 n-butyrophenone 3.592 2.592 2.592 0.259 3077.5 18651763 n-valerophenone 4.317 3.317 3.317 0.262 4343.9 14069855 Tab. 7: Results for 70% acetonitrile, 30% water relative resolution a 12 1.230 R 12 1.513 a 23 1.227 R 23 1.829 a 43 1.280 R 34 2.783 Tab. 8: Results for 70% acetonitrile, 30% water 3.2. Determination of the concentration of an unknown solution of acetophenone with internal standard Acetophenone [μl] Concentration [mg/l] Propiophenone [ml] Concentration [mg/l] 200 20.54 2 20 400 41.08 2 20 600 61.62 2 20 Tab. 9: Concentration of acetophenone and propiophenone in calibration solutions (10 ml). Concentration of the acetophenone starting solution 1.027 g/l, concentration of the propiophenone starting solution 0.1 mg/l. Acetophenone concentration [mg/l] 20.54 41.08 61.62 46.215 2.720 2.709 2.72 2.709 2.720 2.72 2.72 2.709 2.720 2.72 2.709 2.709 average 2.720 2.716 2.716 2.709 standard deviation [min] 0 0.006 0.006 0 2074251 3912784 5466116 4053782 area 1917983 3660184 5550245 4105111 1865558 3578427 5428545 4188340 average area 1952597.33 3717131.67 5481635.33 4115744.33 standard deviation 108567.06 174301.26 62316.61 67906.30 Tab. 10: experimental results for acetophenone Propiophenone concentration [mg/l] 20 20 20 20 4.117 4.107 4.107 4.096 4.117 4.107 4.107 4.096 4.117 4.107 4.096 4.096 average 4.117 4.107 4.103 4.096 standard deviation [min] 0 0 0.006 0 area 2851801 2564238 2419602 2342727 2709309 2392409 2462627 2377062 area
2570436 2340669 2387500 2433199 average area 2710515.33 2432438.67 2423243 2384329.33 standard deviation 140686.38 117036.56 37695.61 45671.72 Tab. 11: experimental results for propiophenone The factor f was calculated with the results of the calibration. The following equation was needed (4) The result for f is: 0.727 ± 0.022. With this value the concentration of the unknown solution was calculated. It is (47.5 ± 3.6) mg/l. 3.3. Quantitative analysis of caffeine in ice tea and espresso 0.045 g/l 0.075 g/l 0.095 g/l espresso Nestea (1:39) peach 3.061 3.168 3.168 3.211 3.157 3.168 3.179 3.211 3.211 3.168 3.168 3.179 3.200 3.221 average time [min] 3.129 3.168 3.175 3.207 3.216 standard deviation [min] 0.059 0 0.006 0.006 0.007 2336359 3918671 4708176 2309601 area 2294937 4249473 5082873 2346478 2234277 2249872 4220363 4372077 2256412 2221463 average area 2293722.67 4129502.33 4721042 2304163.67 2227870 standard deviation 43256.29 183164.51 355572.62 45278.52 9060.87 Tab.12: experimental results for three calibration solutions, espresso (1:39) and Nestea peach A calibration curve has been calculated with the results of the calibration. 6000000 5000000 4000000 y = 5E+07x + 30446 area 3000000 2000000 1000000 0 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 concentration [g/l] Fig. 2: calibration curve of caffeine The calculated concentration of caffeine in espresso is (1.82 ± 0.16) g/l. The calculated concentration of caffeine in Nestea is (43.9 ± 2.3) mg/l.
3.4. Size exclusion chromatography 3.4.1. Calibration of the column with polymethacryl acid (PMA) Polymethacryl acid Humic acid Aldrich Fluka molecular weight [Da] 1270 4030 7750 13.696 12.715 12.352 14.571 14.912 area 98634 325094 639106 - - Tab. 13: experimental values for polymethacryl acid and humic acids, calculated values for the molecular weight of humic acids molecular weight [Da] 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 y = 8E+10e -1.31x Polymethacryl acids Humic acids Expon. (Polymethacryl acids) 12 12.5 13 13.5 14 14.5 15 Fig. 3: calibration of the size-exclusion 3.4.2. Measurement of a humic acid standard Extrapolation for humic acids by calibration curve calculated of the values of the size exclusion: manufacturer formula molecular weight [Da] Aldrich 14.571 8 10.. 410 Fluka 14.912 8 10.. 263 Tab. 14: calculated values for humic acids
4. Discussion 4.1. Influence of the composition of the eluent: qualitative interpretation of the chromatogram of a homolog phenon-series The stationary phase was reverse silica gel a non-polar substance. The molecule in the analyte that is most non-polar stayed the longest in the column. In respect to the time it can be said that it is longer for non-polar molecules than for polar ones. The order of the used substances concerning the polarity is the following: < < < Acetophenone < Propiophenone < n-butyrophenone < n-valerophenone The influence of the composition of the eluent can be seen as the time became shorter the more non-polar eluent (acetonitrile) was used. This can be explained by the fact that the non-polar eluent competes with the substances resulting that the components interact less with the stationary phase what means that it drives faster through the column. This is the reason that usually an opposite polarity of stationary and mobile phase is chosen as the components get separated the better the longer the differences between the times are. 4.2. Determination of the concentration of an unknown solution of acetophenone with internal standard The calculated concentration of the unknown solution is (47.5 ± 3.6) mg/l. The real value is 46.215 mg/l; it is in the calculated range. 4.3. Quantitative analysis of caffeine in ice tea and espresso For espresso there was a value of (1.82 ± 0.16) g/l caffeine calculated. As the concentration of caffeine depends on many factors, there is no definite reference value at all. We found different data such as 30 to 80 mg per cup 1, 50 mg per 50 ml 2, 100 mg per 60 ml 3 and so on. So our measured value is in a reasonable range of these data, we consider it even a little high, what can be explained by its really bad quality. For Nestea Peach we calculated a concentration of caffeine of (43.9 ± 2.3) mg/l. The reference value of the American Beverage Association of 16 mg per 12 ounces (= 45 mg/l) 4 lies in the calculated range. 4.4. Size exclusion chromatography For Aldrich humic acid we found a molecular weight of 410 Da, for Fluka humic acid one of 283 Da. As humic acid is a complex molecule we consider both values as possible. 1 http://www.tippscout.de/weniger-koffein---espresso-oder-filterkaffee_tipp_111.html, 26.5.09 2 http://www.coffeemakers.de/content/view/33/51/, 26.5.09 3 http://sisutraining.wordpress.com/2009/04/29/koffein-zur-legalen-leistungssteigerung/, 26.5.09 4 http://www.ameribev.org/health/caffeinecontent.asp
5. Literature [1] Pimenova, T.; Zhu, L. HPLC Praktikum Skript, Zürich, 2008 6. Appendix 6.1. Spectra 6.2. Lab journal